The overarching aim of this project is to understand the functional neuroanatomy of language and the neurodevelopmental factors that drive that organization. We approach this issue from the perspective of American Sign Language (ASL), a natural language system which includes linguistic structuring similar to that found in spoken language, but which differs radically in terms of sensory and motor modalities. By comparing the neural organization of signed and spoken language, we can explore the effects of modality on the organization of neural networks supporting language in general. Despite the spatialized nature of ASL, our work to date has shown that signed language ability dissociates from non-linguistic spatial and gestural abilities, and relies on many of the same networks implicated in spoken language. Building on these findings, and using a combination of lesion and fMRI methodologies, this proposal focuses on aims in three areas. (1). Neurocognitive Effects of Focal Lesions in Deaf Signers. We aim to build our database of the neurocognitive effects of focal brain injury in deaf signers for both group- and case-study investigations. The database will be a unique resource for a range of theoretical issues. (2). Neural Systems Underlying Sign Language Comprehension. Our aim is to map the neural systems supporting the perception/comprehension of ASL at three levels ("phonemic"/lexical, sentence, and spatialized discourse) and to study their relation to similar non-linguistic perceptual abilities such as motion and form perception, gesture comprehension, and aspects of spatial processing. (3). Neural Systems Underlying Sign Language Production. The aim is to map the neural systems supporting ASL production at these three levels and its relation to non-linguistic manual output and to ASL perception. These studies will clarify the within-hemisphere organization for sign language as well as address recent lateralization controversies about signed vs. spoken language differences. The proposed studies will provide converging evidence from lesion studies and experiments using functional brain imaging to illuminate the neurobiology of language. Mapping the biological organization of language in general, and of signed languages in particular, is central to the concerns of cognitive neuroscience. The research addresses the extent and limits of neural plasticity. Moreover, these studies may directly benefit clinicians, caregivers, and educators by providing crucial information about deaf individuals with brain damage, as well as pave the way to deeper investigations of the neurobiology of language.